Draw oven



Sept. 20, 1938. c. B. FERREE DRAW OVEN Filed Nov. 18, 1956 2 Sheets-Sheet 1 FX.. .vb

INVENTOR @lfm HMM e ATTORNEYS Sept. 20, 1938. c. B. FERREI:4 2,130,420

DRAW-OVEN Filed Nov. 18, 1936 2 Sheets-Sheet 2 LOSS 0F FURN ACE INVENTOR TToRNEY o HEAT |00 200 500 TEMPERATURE O F FURNACE Cil CIO

Patented Sept. 20, 1938 UNITED STATES PATENT OFFICE DRAW OVEN Cliord B. Ferree, Pittsburgh, Pa.

Application November 18, 1936, Serial No. 111,408

2 Claims. (Cl. 26E-5) time successfully and advantageously to draw r` 'Ihis invention relates to the production of forged steel rolls, and consists in a method of procedure, and an apparatus, whereby the possibility is realized of tempering a forged roll by air drawing, with benefits and advantages to be described. This application is a continuation in part of an application for Letters Patent filed by me August 28, 1935, Serial No. 38,195.

In the production of forged-steel rolls, after a roll has been machined and hardened and before polishing for delivery to the user, it is subjected to an ultimate tempering step. This ultimate tempering step, commonly called drawing (in that extreme hardness is in some degree reduced or drawn from the metal), consists in raising the roll from atmospheric temperature to a temperature that in different cases may range from as low as 290 F. to as much as 425, or, in extreme cases, even to 700 or 800, and cooling it again in the open air. This heating of the roll is a very nice operation: it must be accomplished inl very uniform manner, that the quality of the finished roll shall be uniform throughout all its extent. Heretofore this ultimate heating has beenV performed in a bath of oil. Alternative methods of tempering, practised upon other bodies intended for other uses involve, one, the employment of a bath of molten lead, and, another, heating in the gaseous atmosphereof an oven; these two other methods are characterized lead drawing and air drawing. The latter term is inaccurate, in that the atmosphere is not atmospheric air, but krather a gaseous furnace atmosphere; but the term has gained acceptance, and is understood. I shall useV it in accepted manner and my use of it will not be misunderstood. Lead drawing is not appropriate to the ultimate tempering step in the production of a forged roll, be-

cause the melting-point of lead is beyond the temperature range that is requisite; air drawing has not hitherto been .made practical, because of the wide disparity in thermal capacity per unit of volume between steel and air (i. e., furnace atmosphere) and because of the great mass of a roll body, in relation to surface area.

I have discovered that by providing an oven so constructed that the gas burning within shall build up a super-atmospheric pressure in the oven chamber, by forming the furnace walls of material of low heat conductivity, and by burning Within the chamber a gas of high heat value mingled with air in relative quantities such as to effect perfect combustion, I am able for the first time to overcome the diiculties and for the first a forged roll in ain oven. Fig. IV is a chart showing comparatively the heat losses of the apparatus of my invention and those of a tank for oil-drawing.

'Ihe oven is essentially an oblong chamber of approximately square cross-section, and of such particular dimensions as to receive the rolls to be treated. The chamber within is, but for a partition Wall that affords longitudinal subdivision, free of any screen: there is no baille nor flamediverting nor flame-confining partition between, the burner and the article under treatment. The flame has free access to the naked roll surface. Such a chamber I characterize a free chamber. In ordinary circumstances a plant will be required to produce rolls of various dimensions, and the oven will be of suii'icient size to receive the largest. In this instance the oven measures, internally, 16 feet 11 inches in length, 5 feet in breadth, and 5 feet in height. There are within the oven chamber guides that define a space that is 3 feet 9 inches wide; so that this oven is adapted to receive any roll not substantially exceeding 16 feet in length nor 3 feet 6 inches in maximum diameter. I have successfully treated in this oven, having the characteristics herein described, and by following the procedure herein set forth, rolls that ranged in size from 28x55 inches downward. The size given is not a limitation; it happens merely to be the size of the largest rolls I have hitherto had occasion to produce, I have y found it advantageous to provide a removable partition or curtain Wall, subdividing the oven chamber, to the end that for relatively short rolls a portion only of the oven structure need be used; and I have found it convenient thus to reduce the size of the oven by half. size indicated have volume approximately one fourth that of the furnace chamber.

The side walls I and the end Walls 2 are continuous and unbroken and stand permanently fixed upon the floor 3. The roof 4 is preferably too is substantially continuous. The oven y Rolls of the maximum seams in the roof) tight walled, it will be perceived that the play of the ames tends to build up pressure within the oven chamber and to exclude atmospheric air. The practical and actual effect is that an inert atmosphere of high temperature is maintained within the oven; that the actual temperature may by the adjustment of the supply Valves be varied and brought to the desired degree; and that within all the oven chambei` from floor to roof the temperature may be maintained uniform, within a permissible tolerance of ten degrees F.

If natural gas be used, the oven atmosphere will, with inconsiderable variation, be carbon dioxide, 10%; water vapor, 18%; nitrogen, '72%. If fuel gas be used, while the components of the oven atmosphere will be the same, the proportions will be somewhat different.

When in continued operation the roll within the oven has come to furnace temperature, the heating-up burners may be shut off, and the holding burners only continued in action. In case the nozzles of the holding burners are all horizontally placed, the holding burners may have been cooperating with the heating-up burners in their essential function; but in case some of the nozzles of the holding burners are vertically directed, the holding burners will be brought into service in alternation with the heating-up burners.

When the roll has been held at peak temperature the desired length of time (typically fourteen hours), the burners are shut oi, the oven is opened, and the roll removed. While the roll may be brought into the open air at any preferred point in the course of its cooling, it ordinarily will be removed without delay, when the heat treatment is completed. The emptied oven will cool rapidly and will without long delay be available for operation upon another roll.

I have found that at a peak temperature of 350 F., that is to say, with a temperature difference on opposite sides of the wall of 250 or somewhat more, the heat loss in my oven is 55,000 B. t. u. per hour. The heat loss in a tank of comparable size for oil-drawing is 220,000 B. t. u. per hour. A comparative showing of heat loss in the apparatus of the two types throughout the range of ordinary operation is given in the chart, Fig. IV.

The heat generation in my oven to effect what is termed a low draw (the usual procedure) is at a rate that ranges from 45,000 B. t. u. per hour to 226,000, and the average is approximately 80,000 B. t. u. per hour. The saving in heat expenditure over the heretofore prevailing oildrawing practice is about seventy per cent. For high draw in the practice of my invention the heat generation ranges from 45,000 B. t. u. per hour to 457,000. It then will be manifest that in normal operation the heat penetrability of the walls of my furnace is less than 200 B. t. u. per square foot per hour, and that the heat generation within the chamber exceeds 200 B. t. u. per square foot per hour and very considerably exceeds the rate of loss through wall permeability.

The control of temperature is more accurate in the practice of my invention than is possible in the oil-drawing procedure. By actual observation it is found that the variation in peak temperature in the practice of my invention averages 12 degrees F., whereas in the oil-drawing procedure the variation amounts to 22 degrees.

When, as ordinarily will be the case, the roll is removed from the oven immediately on the completion of the heat treatment, the empty oven will in the course of one or two hours have cooled sufciently to allow it to receive another roll for treatment. No such speed of operation is attainable in the oil-drawing procedure.

It is desirable, in order to gain toughness, that a relatively high peak temperature be attained; but a relatively high peak temperature is, in the oil-drawing procedure, gained only with loss of hardness. Actual experience shows that it is possible in my air-drawing procedure to attain higher peak temperatures than in the old oildrawing procedure while maintaining a like degree of hardness.

The oil-drawing procedure is limited, in the matter of peak temperature, by the necessity of operating below the flash-point of the oil. No Such limitation attends my air-drawing procedure.

There are serious disadvantages attendant upon the oil-drawing procedure, from which the air-drawing procedure of my invention is free. The rst and most serious of these is the fire hazard. Operation is in any case and of necessity dangerously near the flash-point of the oil; and because there is variability here that cannot be wholly eliminated, accidents occur, with injury to men and property. It happens inevitably that a roll often carries water to the oil tank, and when this occurs the fire hazard is increased.

The roll as it comes from the oil bath in the oil-drawing operation is coated with oil, and the oil coating delays its cooling to room temperature-and cooling to room 4temperature is necessary, before work upon the roll can be resumed. Furthermore, when at length the roll comes to the grinding wheel, the heavy coating of oil upon its surface clogs the wheel, and necessitates wheel dressing. From all such embarrassments procedure under my invention is free.

I believe myself to be the rst successfully to draw a rolling-mill roll in air.

I claim as my invention:

1. A draw oven for the heat treatment of a rolling-mill roll, including floor, side walls, and roof, the side walls and roof being formed of heat-insulating material of low heat-absorption capacity, the roof being removable and the seams incident to the removable-roof construction affording the sole exit for gas from the chamber within the closed oven, means for supporting by its necks within the chamber and with its face free end enveloped throughout all its extent in the atmosphere within the oven a roll to be treated, and means for projecting into the otherwise free chamber from opposite sides and in a horizontal plane below the lower limb of curvature of a roll supported within the oven chamber two lines of name.

2. A draw oven for the heat treatment of a rolig-mill roll, including floor, side walls, and roof, the side Walls and roof being formed of heat-insulating material of low heat-absorption capacity, the roof being removable and the seams incident to the removable-roof construction affording the sole exit for gas from the chamber within the closed oven, means for supporting by its necks within the chamber and with its face free and enveloped throughout all its extent by the atmosphere within the oven a roll to be treated, and means for developing in the otherwise free chamber in a horizontal plane below the lower limb of curvature of a supported roll an outspread substantially uniform layer of ames.

CLIFFORD B. FERREE. 

